This has been bothering me too so now that you have raised it I finally decided to reregister having long since lost my login details and add some thoughts:
If we assume that DM was the sole perpetrator, LB was killed by gunshot, it happened in DM's bedroom at Maple Gate and it took place during the night of July 3/4, then I have a hard time seeing how DM on his own could have done everything necessary to get the body to the farm.
Firstly, as stated a few times no-one seems to have heard (including neighbours) anything. Next where was the blood - remember how much there was in TB's truck. Then he had to get the body outside somewhere, again without anyone noticing. If the mattress was soaked in blood how did he remove it on his own from his room - wasn't it king size? He then had to wrap the body in the tarp, which would not be easy as you'd have to spread the tarp out fully then roll it with the body to the other side. Finally at some point he would have to load the mattress and the body into a vehicle and probably have to clean up the mess he would have left behind.
And then again which vehicle was he using? That week the Yukon was out of action and he seemed to be using an Olds. My recollection is that the Olds was a convertible and so not really suitable for the purpose. Then there is the reference to the Dodge Caravan, which might just be able to accommodate the mattress. (Btw, have we ever seen pics of either of these vehicles?)
I don't know where this all takes me.
It did cross my mind that DM was the person who was taking Laura on vacation (she thought) and maybe he lured her (alive) to the hangar, on the pretext that he would fly her personally. This would make all of the above tasks easier to conceal - might even explain the plane pic. I can't say I really believe this but who knows?